Bootleg Overdrive Volume and Blend Not Working Correctly

[jvo]

Bootleg Overdrive. The problem I'm having is that the volume and blend knob don't have the expected result and instead I have an always-on distortion and the volume does something but not adjust the volume.

I have tried to make sure that voltages are good to the ICs and transistors (+9v, +18V, and VREF are all good). I double checked component values based on labels, including the potentiometers and they all look good. I have used an audio probe and see that both the volume and blend knobs both work until we get to the trace between R19, R20, and IC 1.2's 6th pin (see picture). It is at this point that the sound is maxed out and saturated.

If I put the probe between R18 and Blend 3, I can adjust how much clean I hear. If I put the probe at R17 and Blend 1, I can adjust the volume up and down given dirty is blended on. So, both pots are doing their job but not after the two 15K resistors (R19/R20).

The only way I deviate from the BOM is C6 from 51p to 47p and R21 from 53K6 to 51K. I actually had 53K7 as a serial resistor (51K + 2K7) in there initially but thought that might be the problem and went with the 51K. I also replaced the 5532 and the 100p since they were in the general area of the problem. No dice.

Any suggestions would be greatly appreciated. Thank you in advance!

 

[fig]

This could be an issue I suppose. It appears as though the resistor is making contact with the blend pot pad. Hope it helps!

 

[jvo]

Great eyes! I’ll take a look to see. Thank you!

 

[jvo]

@fig that was not the issue but that's extremely good looking at it. I appreciate the effort. I might replace the pots in question. They seem okay but they are the only mechanical element that's in that area that might cause the issue.

 

[fig]

That sounds logical. Let us know how that fares.

 

[zgrav]

look at the resistor closest to the B5K pot as well to make sure there is no "extra" connection. if the pots check out OK with the meter (constant rated resistance between legs 1 and 3, variable resistance as expected between 1-2 and 2-3) I would not swap them out right away. Try using some IPA to clean the back side of the board with a toothbrush or something similar and see if that helps.

For the volume pot, what kind of "something" is it doing instead of adjusting the level? Is it acting more like a tone control or changing the amount of dirt in the signal? That can offer a clue as to the problem as well.

Good luck!

 

[jvo]

The pots checked out but I replaced them anyway. I also replaced all of the components after the blend pot (R19, R20, R22, R23, C13). I cleaned the board with IPA as well. No change.

I have a feeling there is a phantom component that is labeled right but has some problem. I'm not sure if posting DC values on the ICs/transistors would help.

 

[jvo]

Oh, to answer your question, when the blend pot is all the way down, the volume goes down as you turn the knob up. I can still hear distortion when the clean blend is all the way up.

I might actually see if I can buy a used moonshine overdrive to make sure that this isn't just how it works but if this is how it is suppose to work, what a weird pedal.

 

[zgrav]

The problem I'm having is that the volume and blend knob don't have the expected result and instead I have an always-on distortion and the volume does something but not adjust the volume.

1. Does anything vary the "always on distortion" you are hearing? If so, what is it?
2. Can you provide a better description of what "something" the volume control does?
3. Is your blend control doing anything? Or does it seem like it does nothing at all?

 

[jvo]

1. Does anything vary the "always on distortion" you are hearing? If so, what is it?

When I turn the drive down, it is less distorted no matter the blend setting. Reading the description of the pedal from JHS, “However on the Moonshine V2 we added a new Clean knob to blend in any amount of clean signal to your tone!”. Maybe the distortion is always supposed to be there and then you are adding clean tone although it is hard to hear over the very loud overdriven tone.

2. Can you provide a better description of what "something" the volume control does?

When the blend pot is all the way down, the volume goes down as you turn the knob up. When the blend knob is all the way up, the volume knob makes no difference.

3. Is your blend control doing anything? Or does it seem like it does nothing at all?

It makes the whole thing louder but maybe because it is adding the clean signal to the dirty signal(?).

 

[zgrav]

Thanks for the description. Adding some clean tone back into the output looks like the right description, since the drive and volume controls only affect the "unclean" channel. Does the diode switch change your sound? How much does the distortion channel clean up when the drive is dialed down?

From the pro shop video at about the 3 minute point it seems like you should be getting a clean signal when the blend is dialed all the way to the right.

When you say "If I put the probe at R17 and Blend 1" do you mean you are putting the ground for the probe at one point? Ideally you ground the probe on your PCB/case ground and just put the tip at whatever place you are checking.

How clean is the sound you are getting on the clean channel? If you leave the ground for your probe connected to circuit ground, does it change the sound you are hearing with the probe tip at the junction of R18/R20 and at R17/R19?

What is the voltage readings/voltage range you get on each side of the blend pot when you are turning the pot?

 

[jvo]

Does the diode switch change your sound?

Yes, it does!

How much does the distortion channel clean up when the drive is dialed down?

It cleans up to where it sounds like a louder version of bypass.

From the pro shop video at about the 3 minute point it seems like you should be getting a clean signal when the blend is dialed all the way to the right.

This is interesting but it doesn't sound like this at all. It sounds like a very loud clean is combined with the distortion not clean overtaking distortion.

When you say "If I put the probe at R17 and Blend 1" do you mean you are putting the ground for the probe at one point? Ideally you ground the probe on your PCB/case ground and just put the tip at whatever place you are checking.

Yes, I ground the jack and then put the sound probe at the location. I was trying to say that when I put it at either point, not both.

How clean is the sound you are getting on the clean channel?

Using the probe at the junction between R18, R20, and Blend 3, it sounds clean. When I put it at the R17, R19, Blend 1, it sound distorted and can adjust the volume with the volume knob like I'd expect.

What is the voltage readings/voltage range you get on each side of the blend pot when you are turning the pot?

I get 8.31vdc (vref) at all three legs no matter if the blend pot is turned up or down. hmmmmm.

 

[zgrav]

I get 8.31vdc (vref) at all three legs no matter if the blend pot is turned up or down. hmmmmm.

I agree that seems odd. Where do you set the vol/level pot for unity? I am wondering if you are just getting too much output from your distortion channel so it overpowers the clean output in the blend.

 

[jvo]

How clean is the sound you are getting on the clean channel?

Using the probe at the junction between R18, R20, and Blend 3, it sounds clean. When I put it at the R17, R19, Blend 1, it sound distorted and can adjust the volume with the volume knob like I'd expect.

I went back to double check this. It is clean before R18 but sounds distorted and is affected by the drive at the junction between R18, R20, and Blend 3. Not sure if that matters.

 

[jvo]

Where do you set the vol/level pot for unity? I am wondering if you are just getting too much output from your distortion channel so it overpowers the clean output in the blend.

Could you please expand on this a little more? My understanding of the pedal (off of this post: https://forum.pedalpcb.com/threads/moonshine-v2-bootleg.4708/) is that no matter what, clean will be there. So, there is no unity volume in the traditional sense. Happy to hear otherwise, though!

 

[zgrav]

The clean signal should always be there because that is also the signal feeding the distortion channel. The issue is not the schematic, since you can find the same schematic here from another source.

I have not built this pedal so I don't know if what you are describing is anything close to how it is supposed to work. It is not how I would think it would be based on the demo, although I did see that the V2 of this pedal said that the gain had also been increased.

When you say "It sounds like a very loud clean is combined with the distortion not clean overtaking distortion." do you mean that you can get a very distorted sound that mixes with a loud clean sound? That might be normal operation for the blend control, and would raise the question of whether your clipped channel is working OK. How much does the sound change over the range of the Drive pot?

After looking at this I would think the volume and drive controls would act like you would expect if you left out the clean signal from the blend control. Louder/softer with the volume and more dirt when the drive is turned up. It would seem odd that there is no other adjustment for the clean channel except for the blend, but I think it is mostly there to enhance the mix and not dominate it.

 

[jvo]

When you say "It sounds like a very loud clean is combined with the distortion not clean overtaking distortion." do you mean that you can get a very distorted sound that mixes with a loud clean sound?

Yes. But on that video, it seems like when he turns up the blend, it is more clean than dirty. In other words one or the other whereas mine is both.

That might be normal operation for the blend control, and would raise the question of whether your clipped channel is working OK. How much does the sound change over the range of the Drive pot?

The drive pot goes from clean to extremely overdrive. That and the tone seem to be working just fine.

After looking at this I would think the volume and drive controls would act like you would expect if you left out the clean signal from the blend control. Louder/softer with the volume and more dirt when the drive is turned up. It would seem odd that there is no other adjustment for the clean channel except for the blend, but I think it is mostly there to enhance the mix and not dominate it.

Agreed.

Thank you so much for your help on this. Again, if I put my audio probe before it gets to the blend knob, everything works like how I'd expect it. The volume, drive, and tone knob all work fine on the dirty channel. The clean sounds clean. Once I get into that area that I originally circled, it sounds really distorted and messy. The only thing I have not completely taken off is the socket for the IC but that seems really unlikely to cause problems but who knows?!

 

[zgrav]

I would check all of the parts on the back side of the board around the IC on the bottom using the meter to see if there are any unexpected connections between the parts. Did the back clean up OK using IPA?

 

[jvo]

I fixed it!

All I had to do was…

…buy another pcb and try again.

I looked and looked and looked at that other board and I didn't see what was wrong at all. Oh well. The new board works like I expect. The blend transitions between clean (unity) and dirty which can be controlled by the volume which goes down to zero.

I appreciate everyone's efforts to help out but sometimes you just gotta pay $12 and deal with it.

 

[zgrav]

Still quite a mystery, but glad you ended up with a working board.